Positive effects of proline addition on the central metabolism of wild-type and lactic acid-producing Saccharomyces cerevisiae strains

Enhanced robustness and fermentation characteristics of lager yeast in high gravity brewing through accumulation of intracellular proline

In beer production, lager yeasts are subjected to harsh environment in high-gravity brewing (HGB, 24°P or more), thus leading to reduced fermentation performance, increased mortality and formation of off-flavors. This study aimed to improve the vitality, viability and fermentation characteristics of lager yeast during HGB through the accumulation of intracellular proline and to reveal the potential mechanism. A mutant lager yeast Y-100 with significantly increased intracellular proline fluorescence intensity of 37.37 % was obtained by Atmospheric and Room Temperature Plasma (ARTP) mutagenesis. Compared to parental YY, the mutant Y-100 had 13.94 % higher intracellular ATP content, 23.01 % lower ROS accumulation and 77.71 % lower mortality rate at the end of serial batch fermentation for 5 times. Moreover, the time for beer matureness by Y-100 strain was shorted by one day while the real degree of fermentation value was 2.76 % higher using 24°P wort. Through genome resequencing, RT-qPCR analysis and gene knockout and overexpression, the up-regulation of GNP1 and SUA7 genes in Y-100 strain might contribute to the proline accumulation in lager yeast cells, thus resulting in energy supply and stress protection for lager yeast during HGB. The results not only provided new insights into the role of proline in lager yeast towards unfavorable industrial condition, but also obtained a high-efficient Y-100 strain for potential HGB application.

Research progress of anti-environmental factor stress mechanism and anti-stress tolerance way of Saccharomyces cerevisiae during the brewing process

Saccharomyces cerevisiae plays a decisive role in the brewing of alcohol products, and the ideal growth and fermentation characteristics can give the pure flavor of alcohol products. However, S. cerevisiae can be affected profoundly by environmental factors during the brewing process, which have negative effects on the growth and fermentation characteristics of S. cerevisiae, and seriously hindered the development of brewing industry. Therefore, we summarized the environmental stress factors (ethanol, organic acids, temperature and osmotic pressure) that affect S. cerevisiae during the brewing process. Their impact mechanisms and the metabolic adaption of S. cerevisiae in response to these stress factors. Of note, S. cerevisiae can increase the ability to resist stress factors by changing the cell membrane components, expressing transcriptional regulatory factors, activating the anti-stress metabolic pathway and enhancing ROS scavenging ability. Meantime, the strategies and methods to improve the stress- tolerant ability of S. cerevisiae during the brewing process were also introduced. Compared with the addition of exogenous anti-stress substances, mutation breeding and protoplast fusion, it appears that adaptive evolution and genetic engineering are able to generate ideal environmental stress tolerance strains of S. cerevisiae and are more in line with the needs of the current brewing industry.

Chemical Constituents and Molecular Mechanism of the Yellow Phenotype of Yellow Mushroom (Floccularia luteovirens)

(1) Background: Yellow mushroom (Floccularia luteovirens) is a natural resource that is highly nutritional, has a high economic value, and is found in Northwest China. Despite its value, the chemical and molecular mechanisms of yellow phenotype formation are still unclear. (2) Methods: This study uses the combined analysis of transcriptome and metabolome to explain the molecular mechanism of the formation of yellow mushroom. Subcellular localization and transgene overexpression techniques were used to verify the function of the candidate gene. (3) Results: 112 compounds had a higher expression in yellow mushroom; riboflavin was the ninth most-expressed compound. HPLC showed that a key target peak at 23.128 min under visible light at 444 nm was Vb2. All proteins exhibited the closest relationship with Agaricus bisporus var. bisporus H97. One riboflavin transporter, CL911.Contig3_All (FlMCH5), was highly expressed in yellow mushrooms with a different value (log₂ fold change) of −12.98, whereas it was not detected in white mushrooms. FlMCH5 was homologous to the riboflavin transporter MCH5 or MFS transporter in other strains, and the FlMCH5-GFP fusion protein was mainly located in the cell membrane. Overexpression of FlMCH5 in tobacco increased the content of riboflavin in three transgenic plants to 26 μg/g, 26.52 μg/g, and 36.94 μg/g, respectively. (4) Conclusions: In this study, it is clear that riboflavin is the main coloring compound of yellow mushrooms, and FlMCH5 is the key transport regulatory gene that produces the yellow phenotype.